Hmm, doesn't look very good does it, especially with news reports bandying about the word 'meltdown', which isn't even remotely likely.

Shame about this scaremongering really as, despite being a beardedvegansinglespeedcycliststudent, I'm all for nuclear power (qualifier: as a medium-term alternative to fossil fuel-fired power stations).

Sorry, can't actually answer your question, but if unlooked for opinions weren't given at every opportunity, this wouldn't be Singletrack

So the back up generators have been flooded and the water is no longer circulating.
The steam pressure rises until a pipe bursts, or more likely, a pressure relief valve opens, the steam escapes in to the much larger volume of the containment building.
Where's the problem ?

As far as I understand it, nothing's "going wrong" as it were, apart from the bleeding obvious. There's a chain of safety measures and each "newsflash" we hear about is just one more step along the chain. They're depressurising now so they can use the low-pressure cooling system. I think they possibly knew they would have to go this far along the chain quite some time ago, hence the urgent need for coolant that we've been hearing about on the news.

Until the media stops being hysterical we will not know what is happening.
But the fact is water has wrecked a lot of stuff, water in electrics is not good.Think we all understand that bit.
The ground has opened up and swallowed whole parts of the country, doubt if it discriminates against a nuclear plant or bedding plants!!
One thing is certain, Japan and NZ will be rebuilt before Haiti

Well the news is pretty convinced it's the reactor that exploded. There's some before/after film of a big square building, aka the containment building blowing itself to bits. It's a pressurised water reactor, so if you can't stick the control rods in or cool it down, I can't see why it wouldn't be the reactor that exploded....

a so called "melt down" should be impossible, if it isnt, someone is going to have to answer some questions with some damn good answers.

In Chernobyl, the rods were lowered into the reactor, in order to make the heat. when the control systems failed, the weight of the rods, held them in the reactor under gravity, and they could be pulled out.

since chernobyl, its been flipped.

the rods default position (due to gravity mainly) is OUT, not IN.
the rods have to be actively held into the core, and if anything goes wiggy, they should fall out due to gravity.

a high tech dead mans handle arrangement.

if they pump that moves the water around the reactor has failed, no one is getting power ANYWAY, so they will just shut it down and it will begin to cool.

surely?!

i would IMAGINE, if the station is "gravity fed", the UN and other such "masters of the universe for the forces of good" are going to have a SHITFIT, though this is just extrapolation.

The fuel rods get hot.
Water gets circulated around them (the "cooling water" that everyone's talking about at the moment).
The water turns to steam and is used to drive a turbine.

The liquid that circulates round the reactor does not turn to gas (it isn't always water) - it passes through a heat exchanger which transfers the heat to the water which vaporises to drives the turbines.

any vented steam, wont be radioactive,
coolant is normally pulled from the sea, and put back into the sea ANYWAY.
quite often to the distress of the environ-mentalists, as the warmer water means we are getting tropical sealife in the small lagoon off our north sea reactors

its going to be pretty unlikely (fingers crossed) that the heat transfer fluids leak.

My guess is the secondary coolant system has over-pressurised and exploded because the backup jenny pumps are flooded. It's a bit radioactive, but not that much to worry about.

The next problem is the primary coolant. The worry is that even with the rods dropped and the reaction slowed right down, the fuel rods warp and melt, dumping pellets on the floor and making the reactor un-recoverable. In essence: Three Mile Island mark II.

I think China Syndrome is where the reactor heat slowly melt through the floor and just keeps going until it hits the mantle.

"This is starting to look a lot like Chernobyl" Walt Patterson, an associate fellow with Chatham House, has told the BBC after seeing pictures of the explosion at the Fukushima-Daiichi nuclear plant. "The nuclear agency says that they have detected caesium and iodine outside the unit, which certainly indicates fuel melting at the very least," he says. "Once you have melting fuel coming into contact with water, that would almost certainly be the cause of the explosion."

The man is holding unused fuel pellets - not especially dangerous. They make these just down the road from me, and I'm not worried. Once the uranium is in a reactor and the chain reaction starts, you get lots of nasty fission products - these are very radioactive, hence all the fuss about storage of spent fuel rods we're having at the moment - highly radioactive for thousands of years.

Edit: I do wonder about the wisdom of putting lots of nuclear reactors in a highly active earthquake zone.

Outer building shell is usually designed to "fail" before the really important containment stuff inside is put at risk of damage - the big outside building is primarily there to keep the weather away from the electrical/mechanical stuff inside of the building. Blast looked to be gas-driven - a high velocity flash of burning gas (hydrogen ?), then lots of dust and debris as the building shell disintegrates, but then no flame or smoke (so little or no fire).